Biaxial coherence length in a nematic π-cell

Hamdi, Ridha; Lombardo, Giuseppe; Santo, Maria P. De; Barberi, R.

doi:10.1140/epje/i2013-13115-y

Cited by 9 publications

(12 citation statements)

References 31 publications

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“…Secondly, our model predicts that the WORS is observable for R ∼ 3.28ξ b is typically tens of nanometre [11]. Recent experimental work in a π -cell geometry, with conventional optical microscopy techniques, suggests that ξ (0) b ∼ 33 ± 9 nm [19]. This would correspond to cell sizes, R ∼ 78 − 138 nm, and such dimensions are widely modelled by LdG approaches in the community.…”

Section: Resultsmentioning

confidence: 75%

“…The same temperature was chosen in [22], where the authors study OR patterns in 'classical' hybrid planar cells. In dimensional terms, this would correspond to a well with R ∼ 120-150 nm [19]. The Dirichlet conditions (see (3.7) and (3.8)) induce an alignment mismatch along the four vertical edges and, consequently, we obtain four line defects along the four vertical edges in the z-direction.…”

Section: Macroscopic Wells Withmentioning

confidence: 91%

“…We take τ = 4, R/ξ (0) b = 4.5, with strong anchoring conditions as in (3.7) and (3.8 ) and no external fields. In dimensional terms, this describes a well with lateral dimensions between 120 and 150 nm [19]. In figure 7a-c, we numerically compute LC equilibria in the absence and presence of locally melted regions, respectively.…”

Section: (E) Interior Defects and The Wors Patternmentioning

confidence: 99%

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Order reconstruction patterns in nematic liquid crystal wells

2014

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We numerically study structural transitions inside shallow sub-micrometre scale wells with square cross section, filled with nematic liquid crystal material. We model the wells within the Landau-de Gennes theory. We obtain two qualitatively different states: (i) the diagonal state with defects for relatively large wells with lateral dimension greater than a critical threshold and (ii) a new, two-dimensional star-like biaxial order reconstruction pattern called the well order-reconstruction structure (WORS), for wells smaller than the critical threshold. The WORS is defined by an uniaxial cross connecting the four vertices of the square cross section. We numerically compute the critical threshold in terms of the bare biaxial correlation length and study its dependence on the temperature and on the anchoring strength on the lateral well surfaces.

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Section: Resultsmentioning

confidence: 75%

Section: Macroscopic Wells Withmentioning

confidence: 91%

Section: (E) Interior Defects and The Wors Patternmentioning

confidence: 99%

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Order reconstruction patterns in nematic liquid crystal wells

2014

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“…The top cell view is presented and disclinations are visualized by plotting regions of relatively strongly suppressed order parameter, which is realized in the cores of defects. The thickness of disclination lines is roughly given by the nematic biaxial correlation length [7,44] The free energies F of the patterns are, in general, different and depend on geometry and LC material properties. For example, for the set of parameters h ξ b = d ξ b = 50, a strong anchoring condition at the master plate and an absence of an external electric field, the excess free energy F [pattern] = F − F n of all patterns is roughly the same (their values differ for less than 1%), where F n determines the free energy of the equilibrium bulk nematic.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Electric field driven reconfigurable multistable topological defect patterns

Harkai

Murray

Rosenblatt

et al. 2020

Phys. Rev. Research

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Topological defects appear in symmetry breaking phase transitions and are ubiquitous throughout Nature. As an ideal testbed for their study, defect configurations in nematic liquid crystals (NLCs) could be exploited in a rich variety of technological applications. Here we report on robust theoretical and experimental investigations in which an external electric field is used to switch between predetermined stable chargeless disclination patterns in a nematic cell, where the cell is sufficiently thick that the disclinations start and terminate at the same surface. The different defect configurations are stabilized by a master substrate that enforces a lattice of surface defects exhibiting zero total topological charge value. Theoretically, we model disclination configurations using a Landau-de Gennes phenomenological model. Experimentally, we enable diverse defect patterns by implementing an in-house-developed atomic force measurement scribing method, where NLC configurations are monitored via polarized optical microscopy. We show numerically and experimentally that an "alphabet" of up to 18 unique line defect configurations can be stabilized in a 4 × 4 lattice of alternating s = ±1 surface defects, which can be "rewired" multistably using appropriate field manipulation. Our proof-of-concept mechanism may lead to a variety of applications, such as multistable optical displays and rewirable nanowires. Our studies also are of interest from a fundamental perspective. We demonstrate that a chargeless line could simultaneously exhibit defect-antidefect properties. Consequently, a pair of such antiparallel disclinations exhibits an attractive interaction. For a sufficiently closely spaced pair of substrate-pinned defects, this interaction could trigger rewiring, or annihilation if defects are depinned.

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“…The scale over which biaxial order extends in a uniaxial medium Downloaded by [University of Sussex Library] at 23:51 18 August 2015 is known as biaxial coherence length and denoted by ξ b [12]. A dynamical numerical model has shown that ξ b ∼ 5 nm for 5 CB close to the nematic-isotropic transition [13] and recent measurements in the π -cell have given ξ b ∼ 30 nm for 5 CB at T = 25 • C [14]. These experimental values are presumably overestimated because of the simplified optical model adopted to extrapolate ξ b , therefore at present the best value for ξ b is in the order of 5-10 nm.…”

Section: Introductionmentioning

confidence: 99%

DSM1-DSM2 Transition Threshold in Turbulent Nematic Mixtures

Pucci

Carbone

Vena

et al. 2015

Molecular Crystals and Liquid Crystals

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When forced by a suitable electric field, calamitic nematics can undergo electrohydrodynamic instabilities and become turbulent. In contrast to isotropic fluid, they present a transition at high forcing from a turbulent regime (DSM1) to a regime characterized by high density of topological defects (DSM2). We study the transition threshold in nematic mixtures with some percent of 5 CB in MBBA. The threshold decreases by increasing the 5 CB concentration, an opposite behavior to what is expected by the increase of dielectric anisotropy. We suggest that the threshold control parameter is the biaxial coherence length, that is of the order of defect size.

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Biaxial coherence length in a nematic π-cell

Cited by 9 publications

References 31 publications

Order reconstruction patterns in nematic liquid crystal wells

Order reconstruction patterns in nematic liquid crystal wells

Electric field driven reconfigurable multistable topological defect patterns

DSM1-DSM2 Transition Threshold in Turbulent Nematic Mixtures

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